The Island was a location seen in A Quiet Place Part II.
Prior to the events of Day 0, it presumably was a residential area which also had a radio station. On Day 0, the military quickly discovered the creature's weakness to water, and attempted to evacuate as many people to the island but only 2 ships where able to reach it safely.
Regan first discovers the possibility of survivors on the island when she heard and located the source of the music being played on the portable radio.
Initially she set out on her own to reach the island but was later joined by Emmet. After convicing him to follow her, they reached the island and met its inhabitants where the leader who explained how they survived in the first place. The next day Emmett walked along the beach where he was horrified to discover one of the boats from the marina; where one of the Death Angels floated over to the island. He ran back to the settelment to warn the inhabitants about the danger when the creature attacked and killed a few residents. Fortunatly, Regan, Emmett and the island leader got in a car and lured it away from the settlement and towards the radio station.